Vacuum pump



Sept. 21, 1965 H. HUBER ETAL.

VACUUM PUMP 3 Sheets-Sheet 1 Filed July 24, 1962 INVENTORS H-HUBER,E-DUVAL amt 0 GfimLAE/m BY 7%! ATTORNE Sept. 21, 1965 H. HUBER ETAL3,207,423

VACUUM PUMP Filed July 24. 1962 s Sheets-Sheet 2 INVENTORSZ H-HUBER;E-DUVAL and 0. Genus/m Sept. 21, 9 H. HUBER ETAL 3,207,423

VACUUM PUMP Filed July 24, 1962 3 Sheets-Sheet 3 1 a a 1 i INVENTORS:H-HUBER, E-DUVAL and D- G am/3a.;

BY W 777. 24

ATTORNE United States Patent 3,207,423 VACUUM PUMP Harry Huber, EugeneDuval, and Didier Grauleau, Paris, France, assignors to CSF--C0rnpagnieGenerale do Telegraphic Sans Fill, Paris, France Filed duly 24, 1962,Ser. No. 2119M Claims priority, application France, Sept. 7, 1961,872,546 3 Claims. (Cl. fill-69) The present invention relates to vacuumpumps operable wit-l1 thermal evaporation of a metal having getteringproperties, that is, to devices connected with the enclosures to beevacuated and intended to improve the vacuum by the adsorption effect ofthe gases on a metal which is evaporated in a continuous manner and thecondensation of which is caused in a thin layer along a wall. Titaniumis generally chosen as suitable metal for this application by reason ofits high chemical activity, particularly insofar as the most commongases are con cerne-d, of the relatively slight vapor pressure of themetallic titanium and of its compounds, and of the stability of most ofthe titanium compounds in the solid form at ordinary temperature.

The evaporation of the titanium may be assured by any known heatingmeans, for example, by the Joule effect or by electron bombardment; theevaporation of the titanium may be controlled by means which depend onthe mode of the heating employed, for example, by varying the heatingcurrent in case of heating by Joule effect, or by controlling theintensity of the electron flow emitted by a cathode with a view tobombard the titanium reserve.

The present invention aims at a pump which has a length of life superiorto that of the pumps of this type known in the prior art with equalityin the pumping speed, or which offers a higher pumping speed withequality in length of life.

Each of these two performance characteristics, namely pumping speed andlength of life which are in reciprocal interrelation may obviously beimproved by increasing or renewing the titanium reserve, for example, byproviding a coil of titanium wire with means for automatically advancingthe wire to the extent of the use thereof. However, such a systemintroduces into the pump movable parts which normally are a source oftrouble and also compromise the security of proper operation of thepump. The present invention, therefore, proposes to improve theindicated performances by another a-ppr-oach, which permits avoiding theintroduction of movable parts into the pump.

The invention is based on the observation that the end of life of thetitanium pump is principally determined .by the separation of the layerof active material condensed on the wall, at the end of a time less thanthe time of exhaustion of the active material. Consequently, the presentinvention provides means to increase this time of separation ordetachment of the condensed active material in such a manner that itbecomes at least equal to the duration of the life of the pumpdetermined by exhaustion of the active material.

A first means in conformity with the present invention consists ingiving to the elements of the pump a geometry such that the deposit ofactive material is as homogeneous as possible over the entire surface ofthe condensation wall. It is obvious in effect that, all other thingsremaining the same, the separation of the active material is favored bythe non-homogeneity of the deposit and will commence at the place wherethe same i the thickest.

This geometry according to the present invention is spherical; accordingto the present invention, the conuse densation wall of the titanium pumpwill, therefore, have a form materializing at least in part the surfaceof a sphere of which other portions of the surface are realized, to theextent of need thereof, by auxiliary shields or screens.

With respect to this sphere, there exist two possibilities insofar asthe disposition of the titanium reserve is concerned, namely:

(a) Its location at the center of the sphere in which case the reservehas the form of a ball; and

(b) Its location at a point of the surface of the sphere in which casethe reserve may be, for example, located in a crucible incorporatedwithin the Walls of the sphere.

'In both cases, the density of deposit along the internal wall of thesphere by the active material evaporated by the reserve is constantaccording to Lamberts law.

A second means to increase the duration of separation consists inincreasing the roughness or unevenness of the internal walls of thesphere, for example, by providing them with grooves.

Accordingly, it is an object of the present invention to provide avacuum pump of the type described herein above which avoids theshortcomings and drawbacks encountered in the prior art by simple means.

It is another object of the present invention to provide a vacuum pumpof the type described hereinabove which has a greater length of lifethan the prior art pumps known heretofore with the same pumping speed ora higher rate of pumping speed with the sam life length.

Still a further object of the present invention resides in the provisionof a vacuum pump which correlates the supply of gettering material to becoextensive with the life expectancy of the other parts without the needof movable parts within the pump.

A further significant object of the present invention resides in theprovision of a vacuum pump operable by thermally evaporating a getteringmetal in which the period of time is effectively increased before thelayer of the active material condense-d along the walls of the pumpbegins to separate therefrom.

These and other objects, features and advantages of the presentinvention will become more obvious from the following description whentaken in connection with the accompanying drawing which shows, forpurposes of illustration only, several embodiments in accordance withthe present invention, and wherein FIGURE 1 is a longitudinal crosssectional view through a first embodiment of a vacuum pump in accordancewith the present invention;

FIGURE 2 is a longitudinal cross sectional view through a secondembodiment of a vacuum pump in accordance with the present invention;

FIGURE 3 is a longitudinal cross sectional view through a thirdembodiment of a vacum pump in accordance with the present invention, and

FIGURE 4 is a partial view of a portion of the internal surface of theWalls of any one of the pumps of FIG- URES l to 3.

Referring now to the drawing wherein like reference numerals are usedthroughout the various views to designate like parts, and moreparticularly to FIGURE 1, the pump illustrated therein is incommunication with the evacuated enclosure or vessel (not shown) throughan orifice 1. The pump is thereby fixed to the walls of this enclosurewith the aid of a metallic joint 2. The pump is contained within ahousing constituted by a vat-like receptacle, for example, made ofstainless steel, and forming the condensation walls cooled by a liquidcirculating within the coil 4. According to the present invention, atleast one portion of the wall of the receptacle 3 has, as indicated at5, a spherical configuration flowing through the tubulure 8. The shield7 is dimensioned and disposed in such a manner as to leave a pas-. sageor flow channel between the inside of the sphere and. the orifice 1 andthat, at the same time, the projections coming from the center of thesphere outside of the solid angle occupied by the shield 7, fall alwayson the walls of the receptacle 3. Also, according to the presentinvention, the reserve of the active material as-'. sumes the. shape ofa titanium ball 9; realized, for example, by fusion within vacuum in thecourse of a preliminary operation, this ball 9 being supported by ametallic rod 10, for example, made of molybdenum and leaving across aninsulating passage 11 through a me-. tallic joint 12 incorporated withinthe. walls of the receptacle 3. In order to. realize, for example, aheating by electron bombardment, the rod 10 is carried at an anodepotential by a suitable external source (not shown). For the samepurpose, there is provided a filament 13 supported by two rods .14leaving across the insulating passages 15 through the same metallicjoint 12, these rods 14 being connected to a heater source (not shown)and being carried at the cathode potentialof the source ofvoltage supplyfor the rod v10. The receptacle 3 is carried at a still more negativepotential than the cathode potential by any suitable means.

If the electron current of the, filament 13 is sufiiciently intensettoionizetheresid-ual molecules of gas within the enclosure of the pump,then the'device will function as a pump having a dual effect ofionization and getter as is known in the art; 'Otherwise, an auxiliaryfilament 16 may be provided, supported by the same rods 14 and intendedto emit a current owing to which the ionization will be complete.

The modified embodiment of the pump of FIGURE 2, in which the samereference numerals have been used as in FIGURE 1 to designate analogouselements, differs from the embodiment of FIGURE 1 by the fact that thesource of the active material is no longer' placed at the center of thesphere 6 but instead at a point of the surface thereof, particularly ata lower .point,the orifice 1 being oriented toward the top as intheembodiment of FIGURE 1. The titanium is no longer a molten ball butfills a crucible 17 placed at the level of the spherical walls within anappendage 18 connected to the receptacle 3. The bombardment filament 13is placed in the vicinity of the walls of the crucible 17, :and athermal shield 19 is disposed between the filament 13 and the outside.The auxiliary ionization filament 16 has been placed toward the centerof the sphere but could also be suppressed if the necessity thereof doesnot become noticeable.

FIGURE 3 differs from the embodiment of FIGURE '-1 by 'the fact that theorifice 1 is'oriented toward the bottom, the crucible 17 being disposedas in the preceding embodiment of FIGURE 2 at the bottom of the sphere6. The rod supports a foot portion having several branches 20 from whichis suspended the crucible 17. The joint 12 with the passages 11 andispl-aced toward the top of the spherical wall 5. As in the pre- In allcases, the internal spherical surfaces may be provided with grooves orridges to increase the adherence 4 of the deposit of the activematerial, these grooves being indicated in FIGURE 4 and designatedtherein by reference numeral 21 which shows a view of a portion of theinternal surface 5 that may belong to any one of the pumps of FIGURES 1to 3.. 1

The coil 4 may be brazed 'to the receptacle 3 and cooled by water oreventually by freon from a refrigerating installation.

The passages 11 and 15 may be realized by a seal of pure alumina andtitanium. The joints 2 and 12 may be of the type having a gold, copperor aluminum ring, as is known in the art. 1 g

The operation of the pumps described hereinabove does not requireanydetailed explanation thereofsince it is generally known in the art.Nevertheless, the improved performances thereof are significantlynoteworthy ince they may attain, by means of a suitable dimensioning thefollowing figures:

Minimum pumping speed: 10,000 liters per second. Vacuum limit: less than10 torr,

Length of :life with',permanent pumping at pressures lower than 10"torr, at least 2,000 hours.

While we have shown and described several embodi rnents in accordancewith the present invention, it is; understood that the same is notlimited thereto, but is susceptible of many changes and modificationswithin the spirit and scope thereof as known to a person skilled in theart.. For example,any control means known to a person skilled in the artmay be associated with the heating system for the active metal in orderto increase the temper ature to the extent that the evaporating surfacedecreases by use in such a manner as to conserve a constant evapora tionspeed of the metal and, therefore, a constant pump ing speed. Theheating system by bombardment may itself be replaced by any otherequivalent system without departing from the spirit of the presentinvention.

Thus, it is clear that the present invention is susceptible of manychanges and modifications within the spirit and scope thereof, and wetherefore do not wish to be limited to the details shown and describedherein, but intend to cover all'such changes andmodifications as areencompassed by the scope of the appended claims. I

We claim:

1. A high vacuum pump having an orifice for communication with theenclosure to be evacuated and including means for thermally evaporatinga metal having gettering properties and means for condensing said metalon a wall, said wall having a shape materializing at least in part asphericalsurface, and at least one additional shield having a partspherical surface substantially completing the sphere defined by saidwall surface, said shield being separated from said wall by an intervalforming passage between the inside of said sphere and said orifice.

2. A pump as defined in claim 1, wherein said passage is bounded by wallportions extending from said spherical wall, said wall portions beingshaped and positioned so that the projections of said gettering metalcoming from the inside of said sphere outside of thesolid angle occupiedby said shield fall on said walls.

3. Apump as defined in claim 1, further comprising a plurality ofgrooves of the internal surface of said sphere. I References Cited bythe Examiner UNITED STATES PATENTS 2,920,002 1/ 60 Auwarter 204-298 X l3,056,740 10/62 Holland et al 230*69 X 7 FOREIGN PATENTS 1,095,455 12/60Germany.

LAURENCE V. EFNER, Primary Examiner,

1. A HIGH VACUUM PUMP HAVING AN ORIFICE FOR COMMUNICATION WITH THEENCLOSURE TO BE EVACUATED AND INCLUDING MEANS FOR THERMALLY EVAPORATINGA METAL HAVING GETTERING PROPERTIES AND MEANS FOR CONDENSING SAID METALON A WALL, SAID WALL HAVING MATERIALIZING AT LEAST IN PART A SPHERICALSURFACE, AND AT LEAST ONE ADDITIONAL SHIELD HAVING A PART SPHERICALSURFACE SUBSTANTIALLY COMPLETING THE SPHERE DEFINED BY SAID WALLSURFACE, SAID SHIELD BEING SEPARATED FROM SAID WALL BY AN INTERVALFORMING PASSAGE BETWEN THE INSIDE OF SAID SPHERE AND SAID ORIFICE.